Summary: Biological response modifiers are important drugs used in oncology and among them are the novel antitumor drug Ukrain and the more studied (1 ->3)-beta-D-glucans. The aim of this study was to evaluate in vivo the antitumor and antimetastatic capacity of Ukrain and (1 ->3)-beta-D-glucans in the experimental murine Lewis lung solid tumor adenocarcinoma, metastasizing to lung and relatively resistant to cyclophosphamide therapy Administration of Ukrain was shown to reveal antimetastatic effects in the murine Lewis lung adeno­carcinoma model, possibly due to Ukrain's capacity to stimulate macrophages (according to increased serum chitotriosidase activity as an index of macrophage stimulation). The combination of cyclophosphamide plus Ukrain was also shown to be effective: 20% of mice developed lung metastases and 80% did not have metas­tases, compared with the control group, where 100% of mice developed metastases. Ukrain was shown to sig­nificantly restore serum aspartate transaminase (AST) activity, decreasing toxic effects of tumor bearing in mice with Lewis lung adenocarcinoma. Combined therapy with carboxymethylated (1 ->3)-beta-D-glucan (CMG) plus cyclophosphamide inhibited tumor growth and decreased the frequency of lung metastases. Cyclophospha­mide alone inhibited the growth of primary tumor by 62%, whereas chitocarboxymethylated (1 ->3)-beta-D-glu-can (chitoCMG) was ineffective in primary tumor growth inhibition. Both glucans were found to stimulate the release of tumor necrosis factor (TNF)-alpha from peritoneal murine macrophages. Serum chitotriosidase activ­ity as a biochemical marker of macrophage stimulation in mice treated with Ukrain, CMG and chitoCMG in­creased compared with intact mice.